328 



THE AXATOMY OF CESTODES. 



In regard to their mode of origin, the rule is 1 that the embryos 

 are not developed inside the mother's body, as in the Tcenice, but 

 outside it, and often so slowly that weeks and months elapse between 

 the laying of the egg and the time when they attain their definite 

 structure. Being abundantly provided with granular yolk, the eggs 

 of the Bothriocephali by no means require during their development 

 that continuous supply of nourishment necessary for the less favoured 

 Tcenice. 



But not only do the embryos generally develop in free life, but 

 they usually break forth from the egg on the attainment of maturity, 

 and swim about for a time in water by means of a ciliated mantle, 

 until they begin their future parasitism by migration into a living 

 creature. 



The possession of the ciliated apparatus is indeed the most impor- 

 portant and striking peculiarity of these embryos. We have observed 

 it not only in the different species of Boihriocephalus, but in Trice- 

 nophorus, Liyula, Schistocephalus, &c., and may thus presume that it 

 is widely distributed in the allied species. The cilia are generally 

 of considerable length, and are based upon a firm cuticular mem- 

 brane, which is at some distance from the embryonic body. In 

 young embryos (Fig. 177) the space is occupied by a layer of clear 



and relatively large cells of an 

 almost bubble-like appearance, 

 which have between them nume- 

 rous sharply defined granules 

 with strong refractive power. 

 Older embryos exhibit only the 

 latter, the place of the cells being 

 occupied by a clear fluid. 



This mantle occurs, however, 

 not only in the roving embryos, 

 but also in those which, like the 

 Tcenice, remain in the egg, and 

 are thus of course only adapted 

 for passive migration. We have 

 therefore good reason to con- 



FIG. 178. Embryonic development of 

 Bothriocephalus salmonis (after Kolliker). 

 (x 300.) 



Bothriadse. 2 



sider its presence as an almost 

 universal characteristic of the 

 Yet it will hardly surprise us to learn, from the de- 



1 See on this subject the comparisons of v. Willemoes-Suhm, Zcitschr. f, wiss. Zool., 

 Bd. xxiii., p. 345, 1873. 



a According to v. Siebold, there are, however, some exceptions in regard to this. See 

 Willemoes-Suhm, Zeitschr. f. wiss. Zool, Bd. xxiii., p. 344, 1873. 



